The 47-year-old actor admitted portraying the giant tree creature in James Gunn's Marvel blockbuster, after he lost his Fast And Furious co-star and friend in a car crash, was a "very healthy and therapeutic thing to do."

"When we deal with death, our appreciation for life is represented in so many ways," he explained.

"We appreciate everything that's alive... And this character [Groot] celebrates life, in so many ways. It's the most innocent character I've ever played, clearly, which is why I've kind of been so silly. I'm not talking about heavy issues that I'm usually talking about with the movies I make... I get to have fun!"

Capturing Groot through his limited vocabulary - he only says the words "I am Groot" - and motion capture (with jumping stilts) proved to be a new challenge.

"I was being challenged as an actor, as a thespian - the idea of playing a character without any facial mannerisms or allowing your body physicality to play into the character, and being limited to such a small vocabulary," Vin admitted.

Vin reprises his role as Dom Toretto in Fast And Furious 7, which has wrapped filming. Paul's brothers were drafted in to help complete his unfinished scenes.

"[It] was the hardest film to do - and blessed, because there was such a sense of family and coming back. But surreal," he said.

"You would never imagine that you would ever have to mourn someone so close to you, and simultaneously pretend that they're sitting next to you. It's kind of a strange thing to have to do as an artist, and as a human."